1. Field of the Invention
The present invention relates to a nitride type semiconductor device using a substrate corresponding to a silicon substrate (001) plane rotated 7.3xc2x13 degrees about a [01-1] axis to form by etching a trench portion with a (111) plane of silicon, and effecting crystal growth of a nitride semiconductor film with respect to that trench portion, whereby the semiconductor film has a plane orientation of a (1-101) plane, and a method of fabricating such a substrate. The present invention also relates to a nitride type semiconductor device that has a nitride type semiconductor layer stacked on a silicon substrate having a main plane formed of a plane that is within a range of xc2x15 degrees from a (112) plane in an arbitrary direction.
2. Description of the Background Art
Using nitride semiconductor material of GaN, InN and AlN and a semiconductor of a mixture thereof, light emitting devices with InxGa1xe2x88x92xN crystal as a light emitting layer on a sapphire substrate, GaN substrate, SiC substrate or silicon (111) substrate have been produced. Since the Si substrate is particularly superior than the other substrates by the advantage of providing those of a large area and constant quality at low cost, it is expected that a light emitting device can be produced at low cost by using an Si substrate.
Japanese Patent Laying-Open No. 5-343741, for example, discloses a nitride gallium type semiconductor device formed on a silicon (111) substrate.
When a nitride semiconductor is grown using a silicon (111) substrate, a nitride semiconductor film having a C plane as the growth plane can be obtained. However, the planarity of this epitaxial semiconductor film was not so favorable at the atom level.
For example, in the case where an n type clad layer, a quantum well type light emitting layer formed of InxGa1xe2x88x92xN and a p type clad layer are stacked on such a substrate to produce a semiconductor device of a micro structure, the thickness of the light emitting layer and the In composition are not uniform due to the non-planarity of the film. This unevenness affects the light radiation. Only a semiconductor light emitting device having an emission spectrum of a wide half band width of 40 nm could be obtained. The light output of such a light emitting device was inferior to that obtained from an element on a sapphire substrate or SiC substrate.
In the case where such substrates are employed to produce a GaN type MESFET (Metal Semiconductor Field Effect Transistor) having an electrode of a source, drain and gate formed at a film produced by growing an Si-doped GaN layer through a high resistance layer formed of an AlGaN layer, and furthermore a GaN type MODFET (Modulation Dope Field Effect Transistor) having Si modulation-doped on a GaN channel layer, the abruptness at the channel layer interface is poor due to the low planarity thereof. Therefore, the mobility of the electrons running in the channel layer by the scattering of the asperity was degraded. Therefore, a semiconductor device exhibiting favorable electrical characteristics at the cutoff frequency and the like could not be obtained.
Since a silicon substrate of a large area and of high quality can be obtained at low cost, the usage of a silicon substrate for the fabrication of a nitride type semiconductor device allows a more inexpensive semiconductor device to be obtained as compared to the usage of a conventional substrate.
However, in the case where epitaxial growth is effected to produce a nitride type semiconductor layer on a conventional silicon substrate, it was difficult crystallographically to cut the substrate into a square chip since the silicon substrate has a (111) plane as the main plane. There was a problem that the edge was easily chipped after being cut.
In view of the foregoing, an object of the present invention is to provide crystal growth of a nitride epitaxial film superior in planarity and of high quality using a silicon substrate in a multilayered structure of a nitride type semiconductor by improving the planarity at the atom level to increase the abruptness and improve the photoelectric property of the device.
Another object of the present invention is to prevent chipping at the end plane by rendering feasible the cutting of a semiconductor device having a layered structure of a nitride type semiconductor layer into chips.
According to an aspect of the present invention, a semiconductor device includes a silicon substrate and a compound semiconductor layer formed on a main plane of the silicon substrate and represented by the general formula of InxGayAlzN (where x+y+z=1, 0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa6, 0xe2x89xa6zxe2x89xa61). The silicon substrate includes a trench having as a slope a plane inclined 62 degrees from the main plane of the silicon substrate or a plane inclined in a range of within 3 degrees from the inclined plane in an arbitrary direction. The compound semiconductor layer is formed on the slope.
According to another aspect of the present invention, a semiconductor device includes a compound semiconductor layer represented by the general formula of InxGayAlzN (where x+y+z=1, 0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61). The compound semiconductor layer is formed using a silicon substrate having a main plane constituted by a plane corresponding to a (100) plane rotated 7.3 degrees about a [01-1] axis, or a plane in a range inclined within 3 degrees in an arbitrary direction from the rotated plane. The silicon substrate includes a trench having a (111) plane as a slope. The compound semiconductor layer is formed on the slope.
The  less than 0001 greater than  direction of the compound semiconductor layer is substantially perpendicular to the slope. The compound semiconductor layer has a (1-101) plane as the plane orientation. Having the (1-101) plane as the plane orientation indicates that the plane orientation of the main plane of the compound semiconductor layer is substantially the (1-101) plane.
The semiconductor device is a semiconductor light emitting device having a light emitting layer (active layer). The compound semiconductor layer includes the light emitting layer (active layer). The light emitting layer (active layer) has a (1-101) plane as the plane orientation.
According to a further aspect of the present invention, a method of fabricating a semiconductor device includes the steps of forming at a main plane of a silicon substrate a trench having as a slope a plane inclined 62 degrees from the main plane or a plane inclined in the range within 3 degrees from the inclined plane in an arbitrary direction, and forming a compound semiconductor layer represented by the general formula of InxGayAlzN (where x+y+z=1, 0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61) on the slope.
According to still another aspect of the present invention, a method of fabricating a semiconductor device includes the steps of forming a trench having a (111) plane as a slope at a main plane of a silicon substrate that has a main plane constituted by a plane corresponding to a (100) plane rotated 7.3 degrees about a [01-1] axis or a plane in a range inclined within 3 degrees from the rotated plane in an arbitrary direction, and forming a compound semiconductor layer represented by the general formula of AlxGayInzN (where x+y+z=1, 0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, 0zxe2x89xa61) on the slope.
A plurality of the above-described trenches are formed on the Si substrate. The compound semiconductor layer formed on the slope of each trench may be combined according to the crystal growth.
The fabrication method of a semiconductor device of the present invention can include the step of removing the silicon substrate after the compound semiconductor layer is formed.
A fabrication method of a semiconductor substrate of the present invention includes the steps of forming at a main plane of a silicon substrate a plurality of trenches having as a slope a plane inclined 62 degrees from the main plane or a plane inclined in a range within 3 degrees from the inclined plane in an arbitrary direction, forming a compound semiconductor crystal represented by the general formula of InxGayAlzN (where x+y+z=1, 0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61) on the slope, further growing the compound semiconductor crystal formed on the slope of each trench to combine, whereby a compound semiconductor crystal of a continuous film is obtained, and removing the silicon substrate after the compound semiconductor crystal film is obtained to produce a semiconductor substrate formed of the compound semiconductor crystal.
GaN is a crystal of potent orientation. In the general method, a c axis is oriented perpendicular to the main plane. Therefore, the obtained crystal has the C plane as the main plane. It was difficult to obtain a crystal having a plane differing from the C plane.
The inventors of the present invention carried out various experiments to find out that, by applying a mask of SiO2 partially on a substrate corresponding to a silicon substrate (001) plane rotated 7.3 degrees about a [01-1] axis or a plane inclined in the range of within 3 degrees from the rotated plane in an arbitrary direction, and etching away the open portion without the SiO2 mask to form a trench having a (111) facet in the relationship of 62 degrees from the off oriented substrate (main plane) and growing a nitride type semiconductor film epitaxially at that plane, growing is effected with a (1-101) facet of the GaN type semiconductor as the growth plane.
This facet is extremely superior in planarity. By effecting growth using this substrate, a nitride semiconductor film of high planarity at the atom level is obtained.
Furthermore, by inclining the c axis of the GaN film, the difference in the thermal expansion coefficient between the silicon substrate and this substrate is reduced to suppress the occurrence of cracking.
When the (1-101) facet is employed as the growth plane of the semiconductor light emitting device, the electric field generated by the piezo effect at the interface of the well in the active layer and the barrier layer is reduced by inclining the c axis. Therefore, the carrier recombination of the electron-hole pair is improved to result in a higher light emitting efficiency.
A semiconductor light emitting device formed of an AlGaInN type nitride semiconductor was produced on the above-described semiconductor film. The characteristics of the semiconductor light emitting device were measured. Since the planarity is extremely high even at the active layer and the variation in the layer thickness is small, a semiconductor light emitting device having an emission spectrum of a narrow half band width of 15 nm could be obtained.
According to yet a further aspect of the present invention, a semiconductor device includes a compound semiconductor layer represented by InxGayAlzN (where x+y+z=1, 0xe2x89xa6xxe2x89xa61, 0yxe2x89xa61, 0xe2x89xa6zxe2x89xa61) on a silicon substrate. The silicon substrate has a main plane constituted by a plane in a range of xc2x15 degrees from a (112) plane in an arbitrary direction. The compound semiconductor layer is provided on this main plane. The compound semiconductor layer is preferably formed on the main plane with an intermediate layer there between.
According to yet a further aspect of the present invention, a semiconductor device includes a silicon substrate having a main plane in a range of xc2x15 degrees in an arbitrary direction from a (112) plane, a compound semiconductor layer represented by InxGayAlzN (where x+y+z=1, 0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61) layered on the main plane, a first electrode formed on the compound semiconductor layer, and a second electrode formed at a back side of the silicon substrate.
The inventors carried out experiments taking into consideration the issues set forth below to conceive of the usage of a silicon (112) plane substrate that has a (112) plane as the main plane. The division of a wafer into chips is facilitated when the side planes in the two directions of a square chip has the minimum numbers of silicon bonds in the atomic arrangement of the silicon plane and the silicon atoms are arranged uniformly at that plane without the arrangement of other silicon atoms. A flat epitaxial layer is required using such a plane.
The inventors confirmed that the silicon substrate could be easily cut in the two-axis directions of  less than 11-2 greater than  and  less than 1-10 greater than  when a silicon (112) plane substrate with the (112) plane as the main plane was used. Furthermore, a flat nitride type semiconductor layer could be formed on the main plane by the usage of an intermediate layer (buffer layer).
By stacking an AlGaInN type nitride semiconductor layer on the nitride type semiconductor layer to produce a semiconductor device, the semiconductor device exhibited higher light radiation intensity as compared to the conventional one. By carrying out scribing in the cutting operation into chips, a square semiconductor device chip with no chipping is obtained.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.